System of gas plating



Nov. 16, 1954 P. PAWLYK 2,694,377

SYSTEM OF GAS PLATING Original Filed Oct. 8, 1951 gsheeis-sheet 1INVENTOR PETER PAWLYK 8Y7: 7.1;;

ATTORNEYS SYSTEM OF GAS PLATING Original Filed Oct. 8, 1951 2Sheets-Sheet 2 FIG-2 FIG-.3

INVENTOR PETER PAWLYK BY W Fm ATTORN EYS United States Patent SYSTEM OFGAS PLATIN G Peter Pawlylr, Dayton, Ohio, assignor to The CommonwealthEngineering Company of Ohio, Dayton, Ohio, a corporation of Ohio 2Claims. (Cl. 118-48) This invention relates to a gas plating system andprocess for the production of semi-conductive and non-conductivecoatings on insulating materials and to the products produced by theprocess.

This application is a division of application Serial No. 250,303, tiledOctober 8, 1951, and assigned to the same assignee as the presentinvention.

This application is related to applications, Serial Nos. 250,301;250,302; 250,304; 250,303; 250,306; and 250,307, all filed October 8, 1951, and all by the same inventor as the present application.

it has been round that electrically resistant layers of high quality maybe produced by the formation of the mixed copper oxides, particularlycuprous oxide, on metallic and non-metallic bases for contacting thebase under carefully controlled conditions, tobe more particularlydiscussed hereinafter, with copper acetylacetonate in the gaseous stateto effect decomposition thereof. The process of formation of the oxidesmay be facilitated by carrying out the decomposition in an oxidizingatmosphere to achieve selective oxidation of any deposited metalliccomponent present as decomposition of the copper acetylacetonate occurs.

This invention accordingly contemplates the provision of a unique methodfor the attainment of films of mixed oxides of copper on non-conductivematerials.

The invention also contemplates the provision of unique resistiveelements attained by depositing from the gaseous state mixed oxides ofcopper on non-conductive base materials.-

The method of invention is practiced by heating a dielectric basematerial to a temperature range below that at which copperacetylacetonate will decompose to copper metal and contacting the basematerial with heated vapors of copper acetylacetonate at a ratesufiicient to maintain the temperature of the material below the saidrange and at a pressure substantially equal to that of the atmosphere.Under these conditions the plating deposited on the insulating base willcomprise essentially the mixed oxides of copper.

The resistance characteristics of the deposited layer,

for a given concentration of metal-bearing gas in the plating chamber,will vary with the velocity of gas flow, the higher flow ratescontributing to the formation of a greater proportion of the cupricoxide, although some cuprous oxide will always be present. Similarlylower flow rates may contribute to the formation of more cuprous oxidebut the cupric phase will exist in the coating.

In the preferred embodiment of the invention the copper acetylacetonateis vaporized from the solid compound by contacting the heated solid witha heated inert gas, which gas carries the metal-bearing vapors to aplating chamber. The copper acetylacetonate decomposes at approximately455 F. and accordingly the temperature of the solid compound and theinert carrier gas must be maintained considerably below this temperaturepoint.

The plating chamber to which the heated gas mixture is carried is itselfheated, and the arrangement thereof is such that the workpiece thereinwhich is to be plated is at a lower temperature than the atmospheresurrounding it. This is accomplished by exposing the workpiece in thechamber only to the heat of the flowing gases and to radiation from theelement which heats the chamber. The object to be plated is not itselfheated directly as is normally the custom in the gas plating art.

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2 Preferably control is achieved by regulating the temperature of theflowing gases at a point, spaced slightly from the workpiece, andbetween the workpiece and plating chamber heater.

The hot gases when they strike the workpiece of lower temperature willonly partially decompose, and depending upon the exact conditions of thesystem, a mixture of cuprous oxide and cupric oxide, or a mix containingthe oxides plus a small amount of copper metal will be attained. Forexample, films may be obtained on /2 inch diameter ceramic discs withresistances varying from 10 ohms to substantially infinity. The controlof the resistance is attained primarily by controlling the rate of gasflow over the discs in the plating chamber.

Control of the oxide formation may also be in- 1 fluenced by thebleeding into the system of small amounts of oxygen which tends todevelop cupric oxide formation. As the system will contain both carbondioxide and the carbon monoxide decomposition product, care must beexercised to prevent water vapor or any appreciable amounts of hydrogenbearing carbon compounds forming in the chamber, for mixes of oxygen,

carbon monoxide and carbon dioxide may be rendered slightly explosive inthe presence of such constituents. Normally if the oxygen is introducedas -dry air the presence of the nitrogen of the air will serve as asufficiently effective diluent to prevent any deleterious reactions.

The invention will be more fully understood by reference to thefollowing detailed description and accompanying drawings wherein:

Figure 1 is a schematic representation of the apparatus for the carryingout of one embodiment of the invention;

Figure 2 illustrates a carrier for the objects to be plated; and

Figure 3 illustrates schematically apparatus for the carrying out ofanother embodiment of the invention.

in Figure l the major components of the apparatus utilized to carry outthe invention are indicated at 1, 2, 3 and 4. Numeral 1 indicates asource of carrier gas; the numeral 2 a constant temperature bathcontaining a carburetor and the compounds to be vvaporized; the numeral3 indicates the plating chamber; while the numeral 4 designatesgenerally a recovery system.

The tank 5 of inert carrier gas (carbon dioxide) is provided with avalve 6 and flow meter 34 having conthe carburetor. The carburetor 9 andcoil 8 are each immersed in oil 10 contained in tank 11 and maintainedat a constant temperature by means of heater 12 and the thermostat unitindicated generally at.13. Since such thermostats in themselves are wellknown no detailed description thereof will be given herein.

The bath is also provided with a stirrer 14 actuated through belt 15 mymotor 16. The carburetor contains solid layers of copper acetylacetonate17 and a length of insulated tubing extends from the top of thecarburetor and passes to the gas plating chamber 19 of plating chamberunit 3. v

The connection between tubing 18 and chamber 19 may be madethroughstopper 20 although any suitable means of connection may beemployed, the only requirement being that the seal be gas tight.

Gas chamber 19 is provided externally thereof with a resistance heatingelement 21 provided with electrical energy from a source not shown.Mounted in chamber 19 i; an object carrier 22, more clearly shown inFigure The carrier 22 consists of a rack of insulating materialextending the length of chamber 19 on a wall thereof and having supportsthereon for the carrying of ceramic discs 23 of substantially /2 inchdiameter. Chamber 19 is provided at the remote end thereof with anoutlet in which tubing 25 is secured, the tubing 25 passing directly tothe recovery system 4 where it is secured in the bulb of trap 26. Trap26 is surrounded by cooling water 0 27 contained in tank 28 having inlet2 and outlet 30 for the passage of the cooling water. The remote end ofthe trap 15 provided with tube 31 for the emission of exhaust gases tothe temperature.

Positioned between the constant temperature bath 2 and the plating unit3 in the line 18 is a pump 32 for the mgaintenance of a steady flow ofgases to the cham- In the operation of the apparatus of invention, toattain a resistive coating having a resistance value of approximately300 ohms per centimeter, a ceramic disc or discs 23 are inserted on thecarrier 22 in the plating chamber 19. The resistance heater 21 isadjusted to supply a temperature of about 600 F. within the chamber 19at a point approximately of an inch above the positioned ceramic disc.The temperature of the oil is adjusted to about 375 F.

Under these conditions the valve 6 on tank 5 is open to permit a flow ofcarbon dioxide of about one liter per minute through line 7 and coil 8wherein it is heated to approximately 375 F. The gas then passes intothe carburetor where it contacts the copper acetylacetonate. The copperacetylacetonate having already been subjected to a temperature of 375 F.by means of the oil bath will have built up a considerable vaporpressure and the enterligig CO2 will sweep these vapors out throughtubing As the packing of the copper compound in the carburetor 9 maytend to restrict to some extent the gas flow, pump 32 is actuated toinsure of the steady flow of gas to the plating chamber 19. The gasespassing into chamber 19 at the flow rate specified will contact theobject or workpiece 23 and will tend to maintain the same cool, that isbelow the temperature of the surrounding atmosphere and below thetemperature at the thermocouple 24. The gases under this condition willdecompose and deposit on the cooler workpiece, forming a film consistingsubstantially only of cuprous and cupric oxide. The waste gases togetherwith any undecomposed copper compound will then pass through tubing 25to the trap 26 where the cooling effect of water 27 will cause thecopper acetylacetonate to deposit out from the decomposition vapors, thedecomposition vapors themselves then flow on to the atmosphere.

The time of plating of the above noted process is approximately 30minutes in order to secure a deposit having a resistance of 300 ohms.

In Figure 3 there is shown an embodiment in which there is provided anoxygen inlet to the system. Since the system is otherwise the same asshown in Figure 1 the same reference nmnerals will be employed. In line18 there is shown an inlet 33 for dry air.

In the operation of the system shown in Figure 3 oxygen to the extent of.05 by volume of the plating gases is bled into the system in a drycondition. When the gases passing from the carburetor 9 through line 18containing the dry air from inlet 33 enter the chamber 19 the presenceof oxygen tends to prohibit the formation of any copper metal.

The system of plating of Figure 1 is preferred to that of Figure 3.However in some instances it may be necessary to use a high temperaturein the plating chamber thus raising the temperature of the ceramic tosuch an extent that metallic copper may tend to deposit. In thiscircumstance the air bleed of Figure 3 provides in the chambersufiicient air to convert the copper to copper oxide. Where temperatureconditions in the chamber are lower and more favorable the system ofFigure 1 offers. close control of the deposition and is preferred.

By way of illustration raising the temperature of the object to 650 F.and the temperature of the flowing gas to 400 F. results in asubstantially electrically nonconductive layer after 30 minutes exposureof the insulated object in the system of Figure 1. Thus by adjusting theflow temperature'and/or the chamber atmosphere temperature, it ispossible with relatively small temperature steps to attain layerresistance between 300 ohms and infinity.

A temperature rise in the chamber to 700 F. should 1 be avoided with thesystem of Figure 1 however for metallic copper may then deposit.

The inert gases useful in the system of invention include, as well ascarbon dioxide, argon, helium, nitrogen, etc.

Substantially all materials of heat insulating nature are suitable forthe practice of the invention. Metallic objects however do not ingeneral maintain a sufficiently low surface temperature to permit theattainment of controlled resistive coatings in the fiow ranges presentlyexplored. Flow. rates of between about 1 to 10 liters of carrier gas perminute are however effective with heat insulating materials and aparticular flow condition may be readily chosen in conjunction with aspecific carburetor temperature to attain a desired result.

It will be understood that this invention is susceptible to modificationin order to adopt it to different usages and conditions and accordinglyit is desired to comprehend such modifications within this invention asmay fall within the scope of the appended claims.

I claim:

1. In a gas plating system for the deposition of copper oxides on heatinsulating material the structure comprising a plating chamber having awall, rack means within said chamber extending the length thereof tosupport .an object therein whereby said object is insulated from heattransmitted through the wall of said chamber, to support an object insaid chamber in heat insulated relation with the wall thereof, means tomeasure the temperature of the atmosphere in said chamber at a point .1remote from said rack means, and means to supply a flow of heatedplating gas between said rack means and said temperature measuring meansat substantially aimospheric pressure.

2. In a gas plating system for the deposition of copper oxides on heatinsulating material the structure comprising a plating chamber having awall, means to heat said chamber, rack means within said chamberextending the length thereof to support an object therein whereby saidobject is insulated from heat transmitted through t-- the wall of saidchamber, to support an object in heat insulated relationship with saidwall of said chamber, means to measure the temperature of the atmospherein said chamber at a point remote from said rack means, means to supplya flow of plating gas to said chamber 1,; between said rack means andsaid temperature measuring means at substantially atmospheric pressure,and means to control said plating gas flow rate whereby the temperaturewithin said chamber at said workpiece may be regulated to less than thetemperature at said temperaiiifture measuring means.

1. IN A GAS PLATING SYSTEM FOR THE DEPOSITION OF COPPER OXIDES ON HEATINSULATING MATERIAL THE STRUCTURE COMPRISING A PLATING CHAMBER HAVING AWALL, RACK MEANS WITHIN SAID CHAMBER EXTENDING THE LENGTH THEREOF TOSUPPORT AN OBJECT THEREIN WHEREIN SAID OBJECT IS INSULATED FROM HEATTRANSMITTED THROUGH THE WALL OF SAID CHAMBERS, TO SUPPORT AN OBJECT INSAID CHAMBER IN HEAT INSULATED RELATION WITH THE WALL THEREOF, MEANS TOMEASURE THE TEMPERATURE OF THE ATMOSPHERE IN SAID CHAMBER AT A POINTREMOTE FROM SAID RACK MEANS, AND MEANS TO SUPPLY A FLOW OF HEATEDPLATING GAS BETWEEN SAID RACK MEANS AND